This is a multi-institutional, Intergroup III trial examining the potential chemopreventative effect of finasteride for prostate cancer. Study subjects who are eligible can have no evidence of prostate cancer clinically. Enrolled participants randomize to either placebo or the study drug (Proscar 5 mg daily), which is administered in a double-blind fashion. Participants are followed with yearly digital rectal exams and serum PSA values. All PSA samples are sent to a central lab for processing, and elevated values are evaluated with biopsy. Any cancer detected during the study results in patients being taken off study. The follow-up period will continue for 7 years, after which all study participants will undergo transrectal ultrasound-guided biopsy, and tissues from the biopsy will be processed at a central pathology site. Differential rates, if any, in the prevalence of prostate cancer between the two study groups will be recorded.